WO2010089398A2

WO2010089398A2 - Acoustic absorber, acoustic transducer, and method for producing an acoustic absorber or an acoustic transducer

Info

Publication number: WO2010089398A2
Application number: PCT/EP2010/051520
Authority: WO
Inventors: Willsingh Wilson
Original assignee: Willsingh Wilson
Priority date: 2009-02-07
Filing date: 2010-02-08
Publication date: 2010-08-12
Also published as: CN102362309B; DE102009007891A1; US20120155688A1; US9369805B2; CN102362309A; EP2394265B1; WO2010089398A3; EP2394265A2; AU2010210069A1; AU2010210069B2

Abstract

The invention relates to an acoustic absorber comprising an absorption layer (1a, 1b) composed of an open-pored porous material. According to the invention, the open-pored porous material is flexurally stiff in such a way that the absorption layer (1a, 1b) is stimulated to flexurally oscillate when sound waves impinge on the absorption layer and the absorber can absorb sound waves of a first frequency range because of the inflow of air into the open-pored porous material of the absorption layer and can absorb sound waves of a second frequency range that comprises lower frequencies than the first frequency range because of the stimulation of flexural oscillations of the absorption layer. The invention further relates to an acoustic transducer and to a method for producing an acoustic absorber or an acoustic transducer.

Description

Acoustic absorber, acoustic transducer and method of manufacturing an acoustic absorber or an acoustic transducer

description

The invention relates to an acoustic absorber according to the preamble of claim 1, an acoustic transducer according to claim 44 and a method for producing an acoustic absorber or an acoustic transducer according to claim 54.

It is known from the state of the art to use porous materials for sound deadening open-pore, a "porous" material being understood as meaning a material which has a certain proportion of void inclusions Proportion of the cavities of the material is in flow communication with other cavities. Thus, sound waves can penetrate into the material due to the interconnected cavities of the porous material open porous and at least partially penetrate it.

The energy of the sound waves penetrating into the open-pore porous material is at least partially converted into heat energy in the material, in particular by the fact that the kinetic energy of air molecules connected to the sound wave is converted into heat by friction of the air molecules at the material enclosing the cavities. This absorption mechanism results in shorter wavelengths of sound, i. higher frequency, are absorbed more than low frequencies.

In addition, from the prior art acoustic transducers, for example in the form of area loudspeakers known, but often have a strong non-linear frequency characteristic. The problem underlying the invention is to provide an acoustic absorber for the absorption of sound waves, which can be produced in the simplest possible way and still allows sound absorption over a wider frequency range. The invention is further based on the problem of specifying a method for producing such an acoustic absorber.

Moreover, another object of the invention is to provide an acoustical transducer which can be realized in a simple manner and which enables sound generation and / or sound recording which is as balanced as possible.

These problems are solved by the acoustic absorber having the features of claim 1, by the acoustic transducer having the features of claim 44 and by the method having the features of claim 54. Further developments of the invention are specified in the dependent claims.

Thereafter, an acoustic absorber for soundproofing is provided, which has an absorbent layer formed from an open porous material, wherein the porous porous material is so rigid that the absorption layer is excited upon impact of sound waves to bending vibrations and the absorber due to the influx of air in the open-pore porous material of the absorption layer Sound waves of a first frequency range and by the excitation of bending vibrations of the absorption layer sound waves of a second frequency range, which includes lower frequencies than the first frequency range, can absorb.

Of course, it is also possible that the first and the second frequency range partially overlap. In particular, the properties of the absorption layer can be selected such that the two frequency ranges overlap in a predetermined overlap frequency range in order to produce increased absorption in this region.

The absorption layer thus combines two absorption mechanisms together, namely the typical absorption of an open porous material at higher frequencies with absorption via the excitation of bending vibrations at lower frequencies. In particular, this means that the sound absorption in the lower frequency range, which is due to the excitation of bending vibrations of the absorption layer, is greater than a possibly present in this frequency range low absorption by the flow through the open-pore porous material. Thus, even with only one absorption layer, the absorber is able to dampen sound waves over a wide frequency range, ie it is not necessary, in addition to the porous porous Absorption layer to provide other means for damping the sound waves at lower frequencies. With the absorber according to the invention, two different absorption mechanisms are thus to some extent connected in parallel.

Porous materials include all porous and fibrous materials such as textiles, nonwoven, carpet, foam, mineral wool, cotton, special acoustic plasters, expanded glass granules, and so-called porous materials that absorb sound energy by frictionally converting vibrations of the air particles into heat energy.

Thin porous porous absorption layers such as textiles preferably absorb in the high-frequency range. In order to achieve a broader band and high absorption even with thinner material thicknesses, e.g. several porous porous absorption layers with increasing flow resistance arranged one behind the other. In this case, in particular the layer with the lowest flow resistance of the sound source is turned. This ensures in particular that the absorption layers, which are arranged facing away from the sound source, do not lose their effectiveness through the cover by the other absorption layers.

In particular, the ratio of the flexural rigidity (or mass, thickness and / or dimensions) to the flow resistance of the absorbent layer may be selected depending on the intended application of the acoustic absorber, e.g. To avoid a drone in smaller rooms or a relatively lower frequencies too strong absorption of high frequencies. In particular, by suitable adaptation of the absorption properties of the absorber according to the invention in the lower frequency range, the formation of a "flutter echo", for example when lining rooms with the absorber, can be counteracted.

Furthermore, by absorbing both lower and higher frequency ranges, the inventive acoustic absorber can replace a combination of different types of absorbers, thereby reducing costs, weight and assembly time, for example. However, the acoustic absorber according to the invention can of course certainly be combined with conventional absorber types, for example the absorption layer of the acoustic absorber according to the invention can be used as the end face (muzzle surface) of a Helmholtz resonator instead of the insulating material conventionally used as end face. In one embodiment of the invention, the absorption layer has a bending stiffness B = - ^ - ^ - ₇ in the range of 0.5 to 500 Nm ² , in particular between 200

12 - (l - μ ² ) and 400 Nm ² , for example between 10 and 100 Nm ² or between 10 and 30 Nm ² , wherein as a measure of the flexural rigidity of the absorption layer in particular the product of modulus of elasticity of the material of the absorption layer and its area moment of inertia I (relative to a direction perpendicular to the main plane of extension of the absorption layer) is used (t: thickness of the absorption layer, μ: Poisson number (or "Querkontra ktionszahl")).

In particular, the absorption layer has such a flexural rigidity that the natural frequency of the absorption layer with respect to flexural vibrations is below 600 Hz, in particular below 300 Hz or in particular of 200 Hz.

With respect to directions parallel to the main extension plane of the absorption layer, the absorption layer may have a similar flexural rigidity. However, this is not mandatory, but the bending stiffness with respect to different load directions can of course also be different.

In order to allow greater bending vibration amplitudes without damaging the absorbent layer, the absorbent layer may have increased flexural elasticity, ductility and / or crush resistance, particularly in comparison with conventional absorbers (e.g., having a mineral fiber or open cell foam). For example, the porous-porous material of the absorbent layer is more ductile than glass or rock wool, i. in particular, that the open-pore porous material of the absorption layer has a greater breaking strength than these materials. In one example, the maximum permissible tensile force of the porous porous material of the absorbent layer is at least 10 percent greater than that of glass.

In addition, the absorption layer may have a basis weight in the range of 30 g / m ² to 20 kg / m ² , in particular between 1 to 5 kg or between 1 to 3 kg. However, the basis weight does not have to be constant over the absorption layer, but it may also be location-dependent, ie the basis weight may vary, for example, in the thickness direction of the absorption layer and / or in a direction perpendicular to the thickness direction. In addition, the bulk density of the porous porous material of the absorption layer may be generally location-dependent, ie vary across the absorption layer and not only in the thickness direction. For example, the bulk density of the porous open-pore material increases in the thickness direction of the absorption layer (progressive densification) or increases or decreases from a center of the absorption layer to its (perpendicular to the thickness direction) surfaces. The mass density of the absorption layer may also increase in the thickness direction relative to a first cross section of the absorption layer and decrease with respect to a second cross section which is at a distance from the first cross section. This can also be done alternately, ie viewed along the length or the width of the absorption layer, the mass density of the absorption layer in the thickness direction alternately increases and decreases. In addition, the bulk density can also extend in the manner of a honeycomb structure to increase the stability of the absorption layer.

The "absorption layer" of the absorber is understood in particular to mean a planar structure which extends along a main extension plane and whose dimension perpendicular to the main extension plane is small in relation to the dimensions parallel to the main extension plane In particular, the absorption layer is, for example, at least approximately rectangular, eg with a length between 30 and 150 cm and a width between 30 and 100 cm (with eg a thickness between 5 and 20 mm) Of course, the invention is not limited to a particular shape of the absorption layer, but the shape and dimensions of the absorption layer can be chosen in principle arbitrarily depending on the intended application of the acoustic absorber.

However, the absorption layer does not necessarily have to be flat, but may also extend at least in sections in a curved manner, so that it may be e.g. with respect to a concave or convex surface. Furthermore, it is possible to make an adjustment of the natural frequencies of the absorption layer or a scattering or bundling of the incident sound waves via the strength of the curvature of the absorption layer.

The absorption layer has, for example, a thickness in the range from 0.1 mm to 100 mm, in particular in the range between 3 mm and 20 mm, it being understood that it is not mandatory for the absorption layer to have a constant thickness. It is also conceivable that the thickness is location-dependent, ie it can be in a direction parallel to a main plane along which vary the absorption layer, for example, to increase the sound absorption by increasing the surface of the absorption layer and / or to produce a diffuse sound-reflecting surface (eg by a wave-shaped configuration of at least one surface of the absorption layer). It is also possible for the absorption layer to be flat (ie at least substantially non-curved), but not continuously formed, but for example to have an opening (in particular rectangular or circular). For example, the absorption layer may be designed such that it circulates around a (central) opening in the manner of a frame.

In this context, it should be noted that the absorption layer may also be designed as a component of a basically arbitrary construction, e.g. in the form of a part of a piece of furniture or a sound-absorbing partition or protective wall (for example, as a substitute for a plasterboard). In particular, due to its flexural strength, the absorbent layer can also withstand greater mechanical stress, i. it is characterized, for example, by from a particularly high in comparison with conventional sound absorbers high ball impact safety, shock resistance, resistance to breakage, dimensional stability, dimensional stability, scratch resistance, abrasion resistance, tear resistance and / or elasticity.

In addition, it is possible to make the surface of the absorption layer air- and / or waterproof (or water-repellent), so that the absorber according to the invention, for example, can also be used in environments with increased hygiene requirements and / or increased humidity or moisture.

Further uses of the absorber according to the invention are, for example:

- Speaker membrane and / or microphone membrane (s.u.);

- Duct silencer

- Sound locks

- sound screen;

- sound capsule;

- sound-insulating partition;

- placing the absorber under a wallpaper (in particular an air-permeable glass fiber or textile wallpaper);

- placing the absorber under an air-permeable plaster (hspwerksporig);

Placing the absorber under a veneer (e.g., a microperforated veneer);

- Projection surface and absorber surface, with simultaneous sound radiation;

- Microphone speaker partition;

- Microphone speaker sails.

The absorption layer of the absorber according to the invention can also in particular in conjunction with elastically resilient and / or soft open-pore porous materials (eg via a point, line and / or sheet-like connection area) as a floor covering or used as a substructure of a floor. As a result, a sound absorption can be combined with a vibration isolation or impact sound insulation.

In another embodiment of the invention, the absorption layer has a specific flow resistance in the range of 50-5000 Pa ^* s / m or N ^* s / m ² . In particular, the flow resistance of the absorption layer depends on its thickness and on the porosity of the open-pore porous material, the "porosity" referring to the ratio of the void volume to the total volume (void volume + solid volume) of the material.

For example, for the porosity σ is given:

_ -1 _ r absoiber n p = mass density r wateral

According to another embodiment of the invention, the absorption layer is supported so that it can be excited to piston-like vibrations, i. by sound action, the absorption layer can not only in bending vibration, but also in a piston-like, i. at least approximately rectilinear, oscillation, be excited. This makes it possible to widen the absorption spectrum of the acoustic absorber or even more precisely to a predetermined frequency (or multiple frequencies) or tune a frequency range. For example, the absorption layer can be stored on an air cushion, wherein the mass of the absorption layer as oscillation mass and the air cushion as a "spring" form an oscillatory system Absorber materials can additionally be arranged in the region of the air cushion.

For example, the natural frequency of the absorption layer with respect to the piston-like vibrations is in the range between 10 Hz and 2000 Hz. The natural frequencies of the absorption layer are in comparison with, e.g. between 0.00005 Hz and 200 Hz.

The (eg in the form of a plate formed) absorption layer can for example be loosely inserted into a frame, so that the frame, for example, although a lateral guidance of the absorption layer causes, but it is in a direction perpendicular to its main extension plane back and forth movable. In another variant, no frame is used, but the absorption layer is otherwise stored so that it can perform free bending-like movements, for example, the absorption layer is hung like a lamella. Another possibility is a floating storage of the absorption layer on a (eg elastic) carrier. There are of course other types of Storage of the absorption layer possible, for example, an at least partial clamping of the absorption layer or only a partial laying on or only partial free release of the absorption layer or a combination of different types of storage, see below.

According to another variant of the invention, the acoustic absorber has a mass element connected to the absorption layer for varying the natural frequencies of the absorption layer, wherein the mass element can influence the natural frequencies with respect to the bending vibrations of the absorption layer and / or with respect to piston-like vibrations of the absorption layer. For example, the mass element is designed in the form of one or more material regions and in particular also has a porous material. However, it is also conceivable in principle that the mass element is formed of a non-porous material. In addition to a punctiform configuration of the mass element, in principle any geometries are conceivable, e.g. square, circular, polygonal, knobbed, conical, also in the form of multidimensional patterns and / or fractals. In particular, the mass element also has a plurality of grid-like structures arranged at a predetermined distance from one another.

In addition, the inventive acoustic absorber can have means for generating a restoring force on the absorption layer. These means are used in particular to be able to tune the natural frequencies of bending vibrations of the absorption layer or possibly of piston-like vibrations of the absorption layer on. By way of example, the means comprise an air-filled volume ("air spring") adjacent to the absorption layer, where it is conceivable that the air-filled volume is created only by incorporation of the absorption layer into a cavity or as a cavity and be used as a ceiling panel of a room, wherein the absorption layer is loosely inserted into a ceiling frame, so that behind the absorption layer, ie adjacent to a side facing away from the space of the absorption layer, an air-filled volume is present, in which the absorption plate can move into it ,

According to another variant of the invention, the means comprise an elastic element coupled to the absorption layer. For example, the absorption layer is mounted on this elastic element, in particular point, line, or planar. However, the elastic member may also comprise a mechanical spring formed in another way.

In addition, it is also conceivable that the elastic element is formed by an element made of an open-pore porous material, the spring-like with the absorption layer (in particular in one piece) is connected. For example, the elastic element is formed by bending at least a portion of the absorption layer, so that the elastic element is connected via a resilient curvature with the rest of the absorption layer and extends correspondingly at an angle to the rest of the absorption layer. The angle between the elastic element and the absorption layer can be selected depending on the application (installation situation, mounting options, etc.) of the acoustic absorber, for example in the range between 30 ° and 45 °.

Of course, it is also possible to provide a plurality of elastic elements, e.g. On opposite sides of the absorption layer are connected thereto.

The acoustic absorber according to the invention can also have means for damping bending vibrations and / or piston-like vibrations of the absorption layer. In particular, the damping means can cooperate with the means for exerting a restoring force on the absorption layer or at the same time be realized by this. For example, an elastic element, via which a restoring force can be exerted on the absorption layer, also cause a certain damping of vibrations of the absorption layer.

However, it is also possible that the damping means comprise separate elements, e.g. a damping element attached to a spring connected to the absorption layer. In another variant, the damping means comprise an opening through which air can flow out of an air-filled volume adjacent to the absorption layer, wherein the outflow of air through this opening absorbs energy from vibrations of the air molecules in the air-filled volume which have been excited by vibrations of the absorption layer , can be dissipated.

According to another embodiment of the invention, the open-pored porous material of the absorption layer is in the form of a compacted (and in particular also ductile) nonwoven fabric. A "densified" nonwoven web is a nonwoven material whose surface density has been increased by appropriate means such as needling or crimping, for example, to make the compacted nonwoven multiple nonwoven layers of flexible organic fibers such as aramids or other organic synthetic fibers such as polypropylene, viscose, polyacrylonitrile , Polyamides or polyesters, and repeatedly needled or needled together with needles perpendicular to the nonwoven surface and / or underside and densified.The plurality of interconnected nonwoven layers of the absorption layer may consist of the same fiber material or even at least partially of different fiber materials. In particular, the nonwoven material of the absorption layer is compressed so that it has a flexural rigidity corresponding to the flexural rigidity of a layer of wood or plexiglass having the same dimensions.

It is also possible that the densified web, e.g. by mechanical needling with a perforation (eg in the form of a "microperforation", ie the production of openings with a diameter in the micrometer range) in order to reduce the flow resistance of the compacted nonwoven fabric.This perforation arises in particular from the fact that in the densified nonwoven material additional interconnected cavities arise, so that it is of course also in the perforated and compacted nonwoven material to an "open-pored porous" material.

Furthermore, it is possible to use a nonwoven which has fibers with a larger diameter compared to fibers of a conventional absorber material, so that even with a high compression of the nonwoven, a flow through the absorption layer or at least a flow into the absorption layer is possible.

The absorption layer consisting of a compacted nonwoven can in principle be processed like a conventional solid material plate, e.g. by tacking, nailing, screwing, gluing, gluing, wedging, profiling, structuring, perforating, deforming, dyeing, and / or candling. Methods of making the densified nonwoven layer will be discussed in more detail below.

According to a development, the open-pore porous material of the absorption layer comprises first fibers of a first material and second fibers of a second material. For example, the first fibers are plastic fibers and the second fibers are bicomponent fibers.

In particular, the first fibers have a higher viscosity (as a measure of the interaction of the fiber molecules with one another, ie for the "internal friction" of the fibers) than the second fibers, which can be realized, for example, by the first fibers being synthetic fibers and the second fibers However, it is also conceivable that the first and the second fibers are made of different plastics, thereby producing a flexible, open-pore porous plate which has high flexural elasticity due to the less viscous second fibers and thus reacts promptly to a given sound pressure However, due to the more viscous first fibers, the absorption layer has an internal friction which dampens the excited vibrations of the absorption layer, so that more energy is extracted from a sound field impinging on the absorption layer than when using an absorption layer containing only one viscosity fibers, or when using a conventional absorber.

In particular, the less viscous fibers are able to absorb more energy (in the form of elastic energy) than the higher viscous fibers, while conversely the higher viscous fibers can convert more energy to heat than the less viscous fibers.

By means of the ratio between the proportion of viscous fibers and the proportion of less viscous fibers, the ratio of the bending stiffness of the absorption layer to the damping can be adjusted. Instead of a higher-viscosity fiber type or in addition, another correspondingly viscous binder may also be used, e.g. a viscous liquid.

According to another embodiment of the acoustic absorber, the absorption layer has on one side, which is to be turned to a sound source, a layer for reducing the sound wave attenuation by the open-pored porous material. For example, the layer is produced by melting a surface area of the absorption layer ("skin formation") .This especially has the purpose of avoiding overdamping of higher frequencies, since the air itself as the carrier medium of the sound waves attenuates even at high frequencies more than at lower frequencies However, it is also possible for an additional material to be applied to the surface to form the coating (eg impregnation, adhesion and / or coating) .The absorption layer can also be provided with a porous, air-permeable, light and / or thin plaster application an optically seamless surface can be generated.

In another variant, the absorption layer of the pores of the open-pored porous material has different openings, which in particular have dimensions (for example width or diameter) which is greater than the average pore dimensions of the open-pore porous material. However, it is also possible to create additional openings ("microperforations") whose dimensions are in the range of the pore dimensions.These additional openings can be used to further increase the sound absorption in a frequency range, for example at least some of the openings are slit-like (eg in FIG Form of a micro slot) is formed.

The shape of the openings can in this case also extend in patterns and in a plurality of spatial directions, ie, for example, also have sections which extend at an angle to the thickness direction of the absorption layer. For example, at least one of the openings extends considered single and / or multiple corrugated, rounded, conical, serrated, etc. along the thickness direction of the absorption layer. The openings may also be arranged in elevations (eg, curved or step-like) and / or bulges of a surface of the absorption layer.

At least some of the openings may also be such that they do not completely penetrate the absorption layer but have a depth that is smaller than the thickness of the absorption layer. The depth of such openings may be considered as a resonator neck length of a Helmholtz resonator, wherein the residual thickness of the absorption layer not penetrated by these openings constitutes a flow resistance located immediately at the mouth surface of the resonator necks formed through the openings. An additional damping of these "resonator necks" can thus be omitted.

Resonator necks of a Helmholtz resonator can be e.g. also form in that one edge of the opening protrudes from the remaining surface of the absorption layer. Such a structure may e.g. be generated by an opening is introduced into a survey of the surface.

A Helmholtz resonator may also be made by creating a continuous opening in the absorption layer and forming this opening at least on one side with a sound absorbing layer, e.g. is made identical to the absorption layer of an open porous material, is closed. By way of example, the absorption layer in which the resonator opening is provided is connected via its surface to a further absorption layer, which has dimensions similar to the absorption layer with the resonator opening and runs continuously in the region of the resonator opening. In addition, it is also possible to arrange several such Helmholtz resonator absorption layers one behind the other.

Furthermore, the acoustic absorber according to the invention can have means for generating a tensile stress in the absorption layer in order to be able to vary its bending stiffness. In particular, the means for generating a tensile stress comprise a mechanism (eg a frame) with which the edge (or at least a portion of the edge) of the absorption layer can be clamped and over which the absorption layer can be stretched in the manner of a membrane in order to increase the natural frequencies of the absorption layer change.

According to a further embodiment of the invention, the absorption layer formed by the open-pored porous material is a first absorption layer of the absorber, wherein the absorber has, in addition to the first absorption layer, a second absorption layer likewise formed from an open-pored porous material.

Between the first and second absorption layers, a volume may be formed, e.g. can be filled with air (or any other gas) to cause the already mentioned above air suspension of the absorption layer. In addition, the volume between the absorption layers may be formed such that vibration energy from the absorption layer over the volume, i. via a coupling of the vibrating absorption layer (the "vibration mass") to the air spring, can be dissipated.

In particular, the air-filled volume is configured to be in fluid communication with the environment of the absorber, whereby by discharging and flowing air into the volume, energy from sound waves excited in the air-filled volume dissipates, i. can be converted into heat energy. For example, the air-filled volume is limited by a frame having at least one opening through which there is a flow connection of the air-filled volume to the surroundings of the absorber.

In another variant, in the volume between the first and second absorption layers is an acoustically insulating material, e.g. an open-pore porous material, arranged, which serves in particular in addition to an air filling for damping vibrations (bending and possibly piston-like vibrations) of at least one of the absorption layers.

The two absorption layers may differ in their properties, e.g. also be formed of different porous materials open porous. It is also conceivable that the two absorption layers have different dimensions, e.g. Have thicknesses.

According to another variant, the first absorption layer has a higher flexural rigidity than the second absorption layer, for example in that for the first absorption layer, another porous material is used porous and / or the first absorption layer is thicker than the second absorption layer. In particular, it is also possible that the first absorption layer has a higher basis weight than the second absorption layer.

Of course, it is not mandatory that the two absorption layers differ; It is also possible that two identical absorption layers are provided or at least two absorption layers, which are formed from identical open-pored porous materials. Of course, it is also possible that the absorber is more than two Has absorption layers, wherein the number and the configuration of the absorption layers can be selected depending on the intended use of the absorber. In particular, a plurality of absorption layers of the absorber can also be connected to one another and in particular can be arranged adjacent to one another with their surfaces (which extend perpendicular to the thickness direction of the layers) (sandwich structure). For example, the absorption layers of a sandwich structure can be joined together by gluing, welding, fusing and / or clawing.

In particular, the absorber comprises two layers of the same material or of different porous and porous materials with a relatively thinner layer with a relatively higher densification of the material and with a further relatively thicker layer with a relatively lower densification. For example, the higher density layer faces a sound source, with the higher density layer e.g. has a much higher stiffness than the less densified thicker layer.

Instead of two layers of the same or different porous open-pored materials in a layer of the same material, an areal relatively thinner area with higher compression and / or higher rigidity and a relatively thicker area with relatively less densification and / or less rigidity may be formed. Moreover, the thinner area of the material, which is over-compacted and / or stiffened more highly, can be produced by progressive unilateral compression and stiffening of the material from one side

Furthermore, the different absorption layers can be connected to one another at points or surfaces, preferably by adhesive bonding, fusion, holding together by frames or holding structures of solid materials, foaming of plastic, elastic or rigid foamable materials, spraying or application of liquid or plastically moldable materials.

For example, the absorbing layer facing a sound source is perforated or slit in a relatively higher density and / or stiffer layer. The change in the thickness of the layer facing away from the sound source, i. their configuration in different thickness, in particular affects the range of the absorption effect in the low-frequency range, in particular in the manner of a film or plate resonant absorber or membrane absorber.

In particular, two or more absorption layers are combined, i. h mounted and connected in rows, wherein the density of the second, third or each successive the sound source facing higher density layer a negative influence on the absorption effect by disturbing reflections within the overall structure are avoided. The connection is made, for example, by spot or surface adhesive bonding, fusion, holding together by means of frames or holding structures of solid materials, foaming of plastic, elastic or rigid foamable materials, spraying or application of liquid or plastically moldable materials. By changing the thickness of the less compacted and less stiffened layer or the less compacted or stiffened region, the efficiency in the low-frequency range can be adjusted in the manner of a plate, membrane or film resonator. Due to the open porous property of the thinner sound source facing higher densified and / or higher stiffened layer, however, the penetration of this layer is made possible by the sound waves, so that an optimal absorption is achieved in the higher frequency range. Surprisingly, the combination of such absorption layers enables a significantly broader band absorption effect than known absorbers, in particular conventional plate, film or membrane absorbers, but also a high absorption in the low-frequency range equal to the mode of action of conventional plate, film or membrane absorbers.

Due to the open-pored porous properties of each higher-density and higher stiffened layer, a reduction in the increase by the absorption effect counteracting reflections within the absorber structure is avoided. Upon connection and / or connection of a mechanical vibration exciter to the higher density and / or stiffened layer or frame or support constructions connected thereto, e.g. In addition, the effect that the absorber is the broadband airborne sound radiator.

Furthermore, the absorber according to the invention can also have at least one sound absorption layer, which is not formed from an open-pore porous fiber material (but for example from a foam). It is also conceivable that the absorption layer is arranged on a particularly elastic carrier (eg a carrier plate), wherein the carrier is formed in particular from a porous material. By coupling the absorption layer to the support, vibrations of the absorption layer can be excited by matrix vibrations (compression waves and shear waves) within the support, for example within the skeletal structure of a carrier made of a porous material. Furthermore, depending on the design of the carrier, piston-shaped and / or bending oscillations in the carrier can also be excited, so that the design (eg material, dimensions, type of attachment, type of adhesion) of the carrier with regard to a tuning optimization of the absorption and / or Sound insulation properties of the acoustic absorber according to the invention can be carried out.

The absorber of the present invention may also include one (or more) further air-permeable layer (e.g., a perforated surface or lattice structure) and / or one (or more) other air-enclosing or air-impermeable layers (e.g., a film). The further air-impermeable layer (e.g., steel) may e.g. be coupled (connected) to the absorption layer to produce a layer composite with increased bending stiffness. The further layers can at least approximately have the area dimensions of the absorption layer. However, it is also conceivable that at least some of the further layers (relative to the surface) are smaller than the absorption layer and / or have a different geometry.

According to a further embodiment of the absorber, the absorption layer has a first portion which is movable relative to a second portion, so that e.g. a folding of the layer is possible. In particular, the absorbent layer may also have more than one (e.g., elongate or pointy) hinge, such that the absorbent layer is e.g. accordion-like with uniform or different intervals of the folding can be pulled apart and compressed. In particular, the absorbent layer may be folded over an elongate hinge (or joints) along a line parallel to a side edge of the absorbent layer. A punctiform joint allows a scissor-like fanning of the absorption layer.

By folding and / or fanning the absorption layer, it is particularly possible to adjust the effective flow resistance of the absorption layer, so that the flow resistance of the absorption layer depending on its thickness d, the mass density p ₀ and the speed of sound in air c ₀ for the flow resistance Ξ results:

Here, X is a factor that defines the level of specific flow resistance:

P ₀ -C ₀ When using homogeneous porous absorbers, the height of the flow resistance, or the factor X, would have to be adapted to the respective thickness in the production process. The above variant of the invention makes it possible to adjust the setting of the factor X over the fanning of the absorption layer.

According to a further variant of the invention, the edge of the absorption layer is at least partially stored in a frame. In particular, the edge in the frame can be set so that the edge region (or at least portions of the edge region) of the absorption layer can at least substantially not be excited to vibrate. The "edge" of the absorption layer bounds the absorption layer in a direction perpendicular to its thickness direction, however, the storage of the absorption layer in a frame is not mandatory, as already mentioned above.

According to a second aspect, the invention also relates to an acoustic transducer, with

a movable layer formed of an open-pore porous material and movable to generate sound waves or sound waves, wherein

- The open-pored porous material is so rigid that bending vibrations of the movable layer can be excited, and

- Conversion means for converting an electrical signal into bending vibrations of the movable layer and / or for converting bending vibrations of the movable layer into an electrical signal.

In particular, the movable layer of the acoustic transducer according to the invention, which can be excited in the manner of a speaker or microphone membrane by sound waves to oscillations, be formed analogous to the absorption layer described above, wherein in principle all described embodiments of the absorption layer can be transferred to the movable layer , For example, the movable layer is formed in the form of a compressed nonwoven material.

According to a development of the acoustic transducer, the conversion means comprise a bending vibration generator which is fixed to the movable layer. For example, the bending vibration generator is realized by an electric coil which is in mechanical contact with a surface of the movable layer of the transducer at one end, so that coil vibrations can be transmitted to the movable layer and the movable layer can be excited to bending vibrations or bending waves in the movable one Layer can be generated. In addition, the acoustic transducer according to the invention may comprise means for suppressing reflections of bending waves excited in the movable layer at the edge of the movable layer. By this means, in particular a superposition of the excited in the movable layer bending waves with reflected waves should be avoided in order to obtain a possible trouble-free conversion of sound waves into an electrical signal or an electrical signal in sound waves.

In a variant, the means for suppressing reflections comprise an increase in the thickness of the movable layer towards its edge. It is also conceivable that the means for suppressing include a decrease in the basis weight of the movable layer towards its edge.

Furthermore, the means for suppressing reflections may alternatively or additionally comprise an increase in the porosity and / or the viscosity of the movable layer towards its edge. In addition, the movable layer may form an outer surface of the acoustic transducer, wherein the means for suppressing reflections comprise an increase in the roughness of the surface towards its edge. Moreover, it is possible for the means for suppressing to include a decrease in the bending stiffness of the movable layer towards its edge.

According to another embodiment of the converter according to the invention, the conversion means both for converting an electrical signal in bending vibrations of the movable layer (speaker operation) and for converting bending vibrations of the movable layer in an electrical signal (microphone operation) is formed, wherein the acoustic transducer has switching means over the conversion means from the speaker mode in the microphone mode are switchable. In other words, the acoustic transducer can be operated both as a speaker and as a microphone. Of course, this is not mandatory, but the transducer may also be designed to be e.g. only works as a speaker.

In a further development of this variant of the invention

- The conversion means adapted to operate the acoustic transducer at a first time in the microphone mode for registering a sound field generated by a sound source and at a second time in the speaker mode, and

- To generate in the speaker operation bending vibrations of the movable element in response to the electrical signal generated during microphone operation, that the acoustic transducer emits sound waves that at least partially interfere with the sound field of the sound source. According to this, the transducer according to the invention can be used, for example, for active noise abatement, aiming at extinguishing the sound waves generated by the sound source as completely as possible, ie sound waves are to be emitted by the transducer which destructively interfere with the sound field of the sound source However, it is also conceivable that an extinction of the sound field should not be effected, but in general a change of the sound field, eg to adapt the sound field to acoustic conditions of a room.

By integrating the electro-acoustic transducers (microphone and loudspeaker), the sound-absorbing effect of the movable element can be expanded and increased. For example, the existing vibration modes of the movable element are electroacoustically amplified.

The invention also relates to a method for producing an acoustic absorber or transducer, in particular according to one of the preceding claims, with the steps:

- Providing a layer of material (in particular in the form of a nonwoven); and

- Compressing and / or foaming the material layer until it is so rigid that it is excited upon impact of sound waves to bending vibrations.

In particular, the material layer is used as the "absorption layer" in the above-described acoustic absorber according to the present invention. Accordingly, the material layer can be densified or foamed until it has a flexural rigidity of 10 to 100 Nm ² , especially between 10 and 30 Nm ² the layer is densified or foamed so far that their lowest natural frequency with respect to bending vibrations is below 300 Hz.

For example, in order to achieve the most uniform pore sizes possible (cavity sizes, the voids formed between the fibers of the nonwoven web), the material layer has multilayer fiber webs, in particular of highly flexible organic fibers, for example of organic synthetic fibers such as polypropylene, viscose, polyacrylonitrile, polyamides or Polyester.

According to a variant of the method according to the invention, the compression of the material layer formed from a nonwoven fabric by needling and / or pressing takes place. For example, the material layer, which may consist of several nonwoven layers, as mentioned above, is first needlepunched several times with needles perpendicular to the nonwoven plane above and / or underside. However, it is alternatively or additionally also possible for the nonwoven layers of the material layer to be connected to one another and / or pre-consolidated in another way. Furthermore, for bonding the nonwoven layers and / or the fibers of the nonwoven layers or for pre-compaction (before a subsequent pressing) of the individual layers, a binder, for example in liquid form or in the form of latex and / or a thermally activatable binder, for example in the form of bicomponents Fibers are used.

For final stiffening, the nonwoven material layer can be compressed by means of a press to the desired stiffness and compressed in this way. After pressing, the material layer can be needled again and pressed again after this re-needling. Of course, the steps of needling / crimping the material layer may be repeated as often as necessary for the desired flexural rigidity and / or air permeability of the material layer. By this method, e.g. produce a nonwoven material layer having a flexural rigidity, e.g. the flexural rigidity of a wooden panel (e.g., birch or oak), a wood-based panel, or a plexiglass panel of comparable (especially identical) dimensions is equal to or better than that.

In particular, when needling an already precompacted material layer, a feed rate, i. the speed at which the material layer is passed through a needle device, which is significantly lower than the feed rates used in the needling of a conventional nonwoven fabric. In particular, a feed rate in the range of 0.50 m / minute to 3 m / minute, in particular between 0.5 m / minute and 2 m / minute is used.

In particular, the needling of the material layer after compression may serve to create a perforation (in particular a microperforation) or a partial perforation in the densified material layer, i. to increase the number of interconnected voids between the fibers of the layer to reduce the flow resistance of the material layer. It is also conceivable that, instead of a nadein, perforation or partial perforation of the material layer may be effected by other mechanical methods (e.g., drilling, water jet perforation) and / or thermal methods (e.g., hot needling, laser perforation).

Finally, the elasticity of the material layer can also be changed (in particular increase) by needling and / or calendering, for example. It should be noted that as the material of the material layer in particular nonwovens are used, which have a high breaking strength, so that bending vibrations of high amplitude can be excited in the material layer, without damaging the material layer. For example, fleeces are used whose fibers have a suitable length (eg at least 40 mm) and which are sufficiently elastic and unbreakable. As already mentioned above in connection with the absorption layer, the material layer can in particular have different types of fibers and / or nonwoven layers which are formed from different types of fibers. For example, a fiber of a second type of fiber (eg, a viscosity different from the first type of fiber) can be mixed with a starting material of a first fiber type.

Moreover, it is also conceivable that in addition (or instead of different viscous fiber types) another viscous material is added, which has a higher viscosity than the fibers of the nonwoven material layer, in particular to influence the resilience of the material layer under bending stress. For example, this can achieve greater energy absorption and damping of vibrations of the material layer, i. the provision for a flexurally elastic stress of the material layer is carried out with an increased inertia, so that the vibrations of the material layer and thus a sound field acting on the material layer more energy is withdrawn.

It is also possible that the densified material layer is thermoformed to bring it into a desired shape for an acoustic absorber. The fibers of a nonwoven used to produce the material layer may also have a coating or be provided with a coating during the production of the material layer. For example, it may be a soil-repellent coating of the fibers and / or a coating for coloring, flame retardance, odor control, increase in hydrolysis resistance, UV protection, soil repellency, water repellency of the fibers, e.g. a plasma polymer functional coating, a Teflon coating and / or a nanocoating comes into question.

In addition, it is pointed out that residues of the nonwoven materials used during the production of the material layer can be recycled and, in turn, serve as starting material for producing a further material layer. For this, the wastes are e.g. shredded and then processed according to the method described above for producing the material layer.

For example, the absorption layer has open-cell foams, fiber materials, minerals, glass materials, ceramics, plastics, but also solid materials such as cellular concrete or the like. The term "glass" covers glass itself and also all glass-related building materials, such as Plexiglas, acrylic glass, organic glass, such as crystal glass. A "plastic" is, for example, PVC, polyethylene, polypropylene, polyester, polystyrene including glass fiber polystyrene, rubber, rubber, including natural rubber, in particular foams of plastics and plastic films of the abovementioned materials, however, the absorption layer may also include metal such as aluminum, lead, Including copper, brass, iron, steel including refining forms such as stainless steel and steel alloys and cast steel, malleable cast iron, sintered metals such as zinc, tin, gold and platinum.

Of course, it is also possible to produce the absorption layer of paper including paper fibers. But also building materials such as concrete including lean concrete, aerated concrete, lightweight concrete, aerated concrete, reinforced concrete, but also cement including cement screed or natural woods such as spruce, beech, chestnut, oak, lark, maple, ebony, but also processing forms of natural wood such as chipboard, wood wool, hardboard, and plywood can be used according to the invention. The same applies to bitumen and bitumen-like building materials, gypsum including gypsum boards, clays and clays, coconut including coconut fibers as well as mats, cork including natural cork, cork and cork also as mats, fiber wool including mineral wool, felt, wool, basalt wool, animal wool or hair , Rock wool, leather, animal leather as well as artificial leather, soft fiber products

Natural and synthetic materials, artificial and natural resin, including resin with glass fibers and hemp, including in the form of mats. Furthermore, the following substances can be used as layer material:

Magmatic rocks

Plutonite (deep rocks): eg. Granite, gabbro, syenite, diorite, granodiorite)

Volcanic rocks: eg. Basalt, phonolite, porphyry, obsidian, lava, pumice)

Clastic (mechanical) sedimentary rocks: eg. Sandstone, conglomerate, breccia, shale, tuff, molasse

Chemical sedimentary rocks: eg. Limestone, shell limestone, dolomite, chalk, rock salt, potash, gypsum

Biological (biogenic) sedimentary rocks: eg. Peat, lignite, hard coal

Metamorphic rocks

Paragesteine (from sediments) & Orthogesteine (from magmatites): eg. Marble, slate, greenschist, fruit shale, quartzite, sericite gneiss, phyllite, mica schist, gneiss mica schist, granulite, gneiss All of these materials may preferably be used in perforated, microperforated, porous sintered or expanded form to produce the porous open porous layers. Furthermore, it is possible to split these materials or comminuted and then reassembled, for example pressed, for producing an open-pore porous structure as a circular capillary, split capillary or microcapillary skeleton structure, in particular by gluing or partial fusion.

In a further preferred embodiment of the invention, the abovementioned materials are coated with liquid materials, such as, for example, paint, which is used to produce open-pore porous structures by the spray method. The pot life must be adjusted when pigmented application or application with admixtures of dissolving or air space forming binders.

The invention is explained in more detail below with reference to embodiments with reference to the figures. Show it:

Figure 1A to 1 G different variants of the acoustic absorber according to the invention;

Figures 2A to 2D further variants of the acoustic absorber according to the invention;

FIGS. 3A and 3B show further exemplary embodiments of the acoustic absorber according to the invention;

FIGS. 4A and 4B different possibilities for the storage of the absorption layer of the acoustic absorber according to the invention;

FIGS. 5A to 5D show further embodiments of the acoustic absorber according to the invention; FIGS. 6A to 6C show acoustic absorbers according to further embodiments of the invention; FIG. 7 shows a diagram of the sound absorption behavior of the air;

FIG. 8 shows a diagram of the absorption behavior of different open-pored porous materials;

FIG. 9 shows a further embodiment of the acoustic absorber according to the invention;

FIGS. 10A to 10D variants of an acoustic absorber according to the invention with a perforated absorption layer;

FIG. 11 shows a further embodiment of the acoustic absorber according to the invention;

Figures 12A to 12E further embodiments of the acoustic absorber according to the invention;

FIGS. 13A to 13C show variants of the absorption layer of the acoustic absorber according to the invention;

FIG. 14 shows a further embodiment of the acoustic absorber according to the invention; and

Figure 15 movable element of the acoustic transducer according to the invention.

FIGS. 1A to 1 D each show a plate-shaped absorption layer 1 of the acoustic absorber according to the invention, the absorption layers each having a continuously varying mass density. According to the example of Figure 1A takes the mass density of the open-pore porous material in the thickness direction of the absorption layer 1 to continuously, that is, the mass density is continuously from a first side 1 1 (eg, to turn to a sound source) to one of the first side opposite second side 12 of the absorption layer 1 smaller.

In the example of FIG. 1 B, the mass density of the absorption layer towards the center (viewed in the thickness direction) continuously increases, while according to FIG. 1C, the mass density decreases continuously towards the center of the layer. According to the embodiment of Fig. 1D, the mass density changes periodically in a direction transverse to the thickness direction of the absorption layer, i. along a direction parallel to the main extension plane of the absorption layer.

Other possibilities of the embodiment of the absorption layer 1 are shown in FIGS. 1 E to G. According to FIG. 1 E, the absorption layer is not designed in a planar manner, but instead has a rib structure 100 at least in sections. In the example of FIG. 1 F, the absorption layer is wave-shaped. Furthermore, it is conceivable that the absorption layer 1 has a honeycomb structure at least in sections, in particular in order to increase its stability.

Furthermore, it is also possible that the absorption layer 1 has a base body 13 (rectangular in cross-section, for example) from which structures 131 (for example periodically arranged) are rectangular in cross-section (FIGS. 2A and B). According to FIGS. 2C and D, a plurality of structures 132 with a curved surface protrude from the main body. As a result, at least one side of the absorption layer has a rib structure as in FIGS. 2A and B or wave structure according to FIGS. 2C and D.

Of course, the variants of FIGS. 1A to 1 G and 2A to D can also be combined with each other.

FIGS. 3A and B relate to a further embodiment of the absorber according to the invention, wherein FIG. 3A shows the absorber in a view from above and FIG. 3B shows the absorber in a perspective view. After that, an absorption layer 1 is mounted in a support frame 2. In particular, the storage of the absorption layer in the frame can take place such that an air volume which acts as a spring coupled to the absorption layer is present on a rear side of the absorption layer facing away from a sound source.

However, instead of or in addition to a rear air cushion other elastic elements can be coupled to the absorption layer of the absorber. This is in Figs. 4A and 4B illustrate. According to FIG. 4A, a plurality of spring elements 3 are arranged on a rear side 12 of the absorption layer, wherein the spring elements are positioned so close to one another that a sheet-like mounting of the absorption layer is produced. Instead of a plurality of closely juxtaposed individual spring elements, it is also possible to use a large-area elastic element which is, for example, approximately over the entire surface of the back of the absorption layer coupled thereto.

Another possibility of the resilient mounting of the absorption layer 1 is shown in FIG. 4B. Thereafter, a plurality of spring elements 3 are arranged spaced from each other, wherein in each case one side of the spring elements is coupled to the back of the absorption layer 1. By this arrangement, the spring elements 3, in particular a punctiform storage of the absorption layer 1 can be realized.

According to the variants 5A to D, a mass element 4 is applied to the actual absorption layer 1, which is formed in particular from a different material than the absorption layer. The mass element serves, in particular, to tune the natural frequencies of the absorption layer 1. The mass element may have a basically arbitrary geometry, e.g. lattice-like (according to the sectional view of FIG. 5A or the plan view of FIG. 5B) or diamond-like (FIGS. 5C and D). According to FIG. 5C, the mass element 4 is arranged at least partially in recesses of the surface of the absorption layer 1.

Figures 6A to C relate to further embodiments of the absorber according to the invention. Thereafter, an absorption layer 1 of the absorber is mounted on a frame 2, that between a bottom portion 21 of the frame 2 and a back side 12 of the absorption layer 1, an air volume 5 is present, which acts as an elastic element and together with the absorption layer 1, a mass-spring -System forms, which can be excited by the action of sound waves on a front side 1 1 of the absorption layer 1 to vibrate. The frame has, in addition to the bottom plate 21 side walls 22 which project perpendicularly from the bottom plate 21 and a side edge 14 of the absorption layer border.

The absorber according to the invention may also have other means for generating a restoring force on the absorption layer, in particular, the side walls of the frame may be formed elastically. It is also possible for the absorption layer 1 to be coupled to elastic elements, for example in the form of a spring 3 or an elastic wall 31, which absorb a vibration of the absorption layer. In particular, the elastic elements are in the region of their side edge 14 with the absorption layer coupled, for example, two elastic elements are provided, which are coupled at opposite side edge portions of the absorption layer with this; see. Fig. 6B and C.

FIG. 7 illustrates the sound absorption behavior of air in relation to different air volumes. According to this, in particular at higher frequencies (approximately from 2000 Hz), air has an increased sound absorption compared to lower frequencies. In order to avoid overdamping in this higher frequency range, the absorption layer of the absorber according to the invention may have on its side facing the sound source a coating 150, e.g. in the form of a "skin", which can be produced by melting a surface area of the absorption layer, see Fig. 9.

FIG. 8 shows the absorption behavior of various conventional porous open-pore absorbers in comparison with the flexurally elastic absorption layer (dots) of the absorber according to the invention. While conventional absorbers absorb much less in the low frequency range (below about 600 Hz) than in the higher frequency range (above 600 Hz), the flexurally elastic absorption layer also absorbs in the region below 600 Hz due to the excited bending vibrations.

For further comparison, the absorption behavior of a plate resonator (triangles) is shown, which absorbs almost exclusively due to excited bending vibrations, i. almost exclusively in the low-frequency sound range, while the absorption layer of the absorber according to the invention absorbs both in the low-frequency and in the higher-frequency range.

In order to further tune the absorption behavior of the absorption layer, it may have a perforation; see. For example, the absorption layer 1 is wave-shaped and has openings 17 on the side flanks of the "wave" (Figure 10A) .It is also possible that the absorption layer has no through openings (Figure 10B), but instead Openings which are covered on one side of the absorption layer (in particular by an insulating material 180), so that in a sense a multiplicity of Helmholtz resonators are formed, and it is also possible to arrange a plurality of such absorption layers one above the other (Figure 10D) formed in elevations 171 of a surface 11 of the absorption layer (FIG. 10C).

According to the embodiment of FIG. 11, the absorption layer 1 is mounted in a frame 2 such that it can be clamped across the frame transversely to its thickness direction in order to tune the natural frequencies of the absorption layer. The exemplary embodiments of FIGS. 12A to E relate to a variant of the absorber according to the invention, according to which two absorption layers 1a, 1b are provided. According to FIG. 12A, the two absorption layers 1 a, 1 b are arranged at a distance and parallel to one another and, in particular, integrally connected to one another via a side edge 1c. In addition, openings 6 can be provided in the side edge 1c, via which air can flow out of a volume 5 extending between the absorption layers 1a, 1b (FIG. 12B).

In addition, an insulating material 7 may be arranged in the volume 5, in particular such that the volume is at least approximately completely filled (FIG. 12C). Of course, the absorption layers 1 a and 1 b need not be integrally connected to each other, but may also each be formed plan without side margin (Fig. 12D), wherein the volume 5 may be filled with an insulating material 7 analogous to Fig. 12C. The insulating material is in particular such that it only partially fills the volume 5 (FIG. 12 E).

Even if the absorber according to the invention has only one absorption layer, it can have an insulating material on its rear side (FIG. 13A). Moreover, it is possible for the absorption layer to include air pockets 8 (Figure 13B) or other, e.g. latticed material 9 (e.g., metal) to increase its flexural rigidity (Figure 13C).

A further embodiment of the absorber according to the invention is shown in FIG. 14. Thereafter, a plurality of absorption layers 1 a-1 d are arranged at a distance and parallel to one another. The absorption layers 1 a-1 d are connected to each other via hinge elements 9, so that the distance of the absorption layers to each other in the manner of a concertina can be changed. The hinge elements may in particular be formed by flexible pieces of material (for example made of a textile material).

Fig. 15 relates to an embodiment of the movable element V of the acoustic transducer according to the invention. The movable member 1 'has a thickness increasing from its center to the side edge 15 (i.e., along the main extension planes of the movable member). This serves in particular to suppress reflections of bending waves excited in the movable element on the side edge.

It should be noted that elements of the above-described embodiments, of course, can be combined with each other. For example, the movable Element of Fig. 15 have elements of the absorption layers of Figs. 1 to 14 (eg an additional mass element or a perforation).

_{* * * * ** * * * *}

Claims

claims

1. Acoustic absorber, with an absorption layer (1) formed from an open porous material,

characterized in that

the open-pore porous material is so rigid that the absorption layer (1) is excited upon impact of sound waves to bending vibrations and the absorber due to the influx of air into the porous material of the porous absorbent layer of sound waves of a first frequency range and due to the excitation of bending vibrations of the absorption layer sound waves a second frequency range, which includes lower frequencies than the first frequency range, can absorb.

2. Acoustic absorber according to claim 1, characterized in that the open-pore porous material is so viscous that bending vibrations of the absorption layer (1) are damped.

3. Acoustic absorber according to claim 1 or 2, characterized in that the absorption layer (1) has a bending stiffness in the range of 0.5 to 500 Nm, in particular between 200 and 400 Nm.

4. Acoustic absorber according to one of the preceding claims, characterized in that the flexural rigidity of the absorption layer (1) corresponds to the bending stiffness of a layer of wood identical dimensions.

5. Acoustic absorber according to one of the preceding claims, characterized in that the lowest bending vibration natural frequency of the absorption layer is in the range between 0.00005Hz and 300Hz.

6. Acoustic absorber according to one of the preceding claims, characterized in that the absorption layer (1) has a basis weight in the range of 500g / m ² to 5kg / m ² .

7. Acoustic absorber according to claim 6, characterized in that the surface mass varies in the thickness direction of the absorption layer (1) and / or in a direction perpendicular to the thickness direction.

8. Acoustic absorber according to one of the preceding claims, characterized in that the absorption layer (1) has a thickness in the range of 0.1 mm to 100 mm.

9. Acoustic absorber according to one of the preceding claims, characterized in that the absorption layer (1) has a flow resistance in the range of 50 to 5000 Pa ^* s / m or N ^* s / m ² .

10. Acoustic absorber according to one of the preceding claims, characterized in that the absorption layer is mounted so that it can be excited to piston-like vibrations.

1 1. Acoustic absorber according to claim 10, characterized in that the natural frequency of the absorption layer (1) with respect to the piston-like vibrations in the range between 10Hz and 2000Hz.

12. Acoustic absorber according to one of the preceding claims, characterized by at least one with the absorption layer (1) connected mass element (4) for changing the natural frequencies of the absorption layer.

13. Acoustic absorber according to one of the preceding claims, characterized by means for generating a restoring force on the absorption layer.

14. Acoustic absorber according to claim 13, characterized in that the means comprise a to the absorption layer (1) adjacent air-filled volume (5).

15. Acoustic absorber according to claim 13 or 14, characterized in that the means comprise an elastic element (3).

16. Acoustic absorber according to claim 15, characterized in that the elastic element (3) comprises a with the absorption layer (1) cooperating mechanical spring.

17. Acoustic absorber according to claim 16, characterized in that the elastic element is formed of an open-pored porous material which is spring-like connected to the absorption layer.

18. Acoustic absorber according to claim 17, characterized in that the open-pore porous material of the elastic element is integrally connected to the absorption layer (1).

19. Acoustic absorber according to one of the preceding claims, characterized by means for damping bending vibrations or piston-like vibrations of the absorption layer (1).

20. Acoustic absorber according to one of the preceding claims, characterized in that the porous material porous in the form of a compacted nonwoven fabric is formed.

21. Acoustic absorber according to one of the preceding claims, characterized in that the open-pore porous material comprises first fibers of a first material and second fibers of a second material.

22. Acoustic absorber according to claim 21, characterized in that the first fibers have a higher viscosity than the second fibers.

23. Acoustic absorber according to claim 21 or 22, characterized in that the first fibers are plastic fibers and the second fibers bicomponent fibers.

24. Acoustic absorber according to claim 21 or 22, characterized in that the first fibers are plastic fibers and the second fibers are metal fibers.

25. Acoustic absorber according to any one of claims 20 to 24, characterized in that the nonwoven is compressed so that it has a bending stiffness in the range of 10 to 50 Nm ² .

26. Acoustic absorber according to one of claims 20 to 25, characterized in that the nonwoven is compressed so that has a lowest natural frequency with respect to bending vibrations which is less than 300 Hz.

27. Acoustic absorber according to one of the preceding claims, characterized in that the absorption layer (1) on a side to be turned to a sound source, a layer (150) for reducing the sound wave attenuation in the higher frequency range by the open-pored porous material.

28. Acoustic absorber according to one of the preceding claims, characterized in that the absorption layer (1) of the pores of the open-pore porous material having different openings.

29. Acoustic absorber according to one of the preceding claims, characterized by means (2) for generating a tensile stress in the absorption layer in order to vary the flexural rigidity.

30. Acoustic absorber according to one of the preceding claims, characterized in that the porous layer formed by the porous material porous absorption layer is a first absorption layer (1 a) of the absorber and the absorber also formed from a porous material porous porous second absorption layer (1 b) ,

31. Acoustic absorber according to claim 30, characterized in that between the first and the second absorption layer (1 a, 1 b), a volume (5) is formed, can be dissipated via the energy of vibrations of the absorption layer.

32. Acoustic absorber according to claim 31, characterized in that in the volume (5) an acoustically insulating material (7) is arranged.

33. Acoustic absorber according to claim 31, characterized in that the volume (5) is filled with air.

34. Acoustic absorber according to claim 33, characterized in that the air-filled volume (5) is bounded by a frame (2) having at least one opening (6) via which there is a flow connection of the air-filled volume to the surroundings of the absorber.

35. Acoustic absorber according to one of claims 31 to 34, characterized in that the first absorption layer (1 a) has a higher flexural rigidity than the second absorption layer (1 b).

36. Acoustic absorber according to one of claims 31 to 35, characterized in that the first absorption layer has a higher basis weight than the second absorption layer.

37. The acoustic absorber according to claim 31, wherein the first absorption layer has a smaller thickness than the second absorption layer.

38. Acoustic absorber according to one of claims 31 to 37, characterized in that the open-pore porous material of the first absorption layer is identical to the open-pore porous material of the second absorption layer.

39. Acoustic absorber according to one of the preceding claims, characterized by a sound absorption layer which has no open-pored porous material.

40. Acoustic absorber according to one of the preceding claims, characterized in that the absorption layer has a first portion which is movable relative to a second portion.

41. Acoustic absorber according to claim 40, characterized in that the first portion is connected to the second portion via a hinge.

42. Acoustic absorber according to one of the preceding claims, characterized in that the edge of the absorption layer is at least partially stored in a frame.

43. Acoustic absorber according to one of claims 1 to 31, characterized in that the absorber is in the form of a frame.

44. Acoustic transducer, with

a movable layer (1 ') formed from an open-pore porous material, which is movable to generate sound waves or by sound waves and in particular according to the absorption layer of claims 1 to 38, wherein

45. Acoustic transducer according to claim 44, characterized in that the conversion means comprise a bending vibration generator, which is fixed to the movable layer.

46. Acoustic transducer according to claim 44 or 45, characterized by means for suppressing reflections of excited in the movable layer bending waves at the edge of the movable layer.

47. Acoustic transducer according to claim 46, characterized in that the means comprise an increase in the thickness of the movable layer towards its edge.

48. Acoustic transducer according to claim 46 or 47, characterized in that the means comprise a decrease in the basis weight of the movable layer to its edge.

49. Acoustic transducer according to any one of claims 46 to 48, characterized in that the movable layer forms an outer surface of the acoustic transducer and the means comprise an increase in the roughness of the surface towards its edge.

50. Acoustic transducer according to one of claims 46 to 49, characterized in that the means comprise an increase in the porosity and / or the viscosity of the movable layer towards its edge.

51. Acoustic transducer according to any one of claims 46 to 50, characterized in that the means comprise a decrease in the bending stiffness of the movable layer towards its edge.

52. Acoustic transducer according to one of claims 46 to 51, characterized in that the conversion means both for converting an electrical signal in bending vibrations of the movable layer (speaker operation) and for converting bending vibrations of the movable layer in an electrical signal (microphone operation) is formed, and the acoustic transducer has switching means, by means of which the conversion means can be switched over from loudspeaker operation to microphone operation.

53. Acoustic transducer according to claim 52, characterized in that

- The conversion means are adapted to operate the acoustic transducer at a first time in the microphone mode for registering a sound field generated by a sound source and at a second time in the speaker mode, and

- In the speaker operation bending vibrations of the movable element in such a manner depending on the electrical generated during the microphone operation Generate signals that the acoustic transducer emits sound waves that at least partially interfere with the sound field of the sound source.

54. A method for producing an acoustic absorber or transducer, in particular according to one of the preceding claims, with the steps:

- Providing a layer of material; and

- Compacting or foaming the material layer until it is so rigid that it is excited upon impact of sound waves to bending vibrations.

55. The method according to claim 54, characterized in that the material layer is designed in the form of a fleece.

56. The method of claim 54 or 55, characterized in that the material layer is compacted until it has a bending stiffness of 0.5 to 500 Nm, in particular between 200 and 400 Nm.

57. The method according to claim 54 or 55, characterized in that the densification of the material layer by needling and / or pressing takes place.

58. The method according to any one of claims 54 to 56, characterized in that the material layer is perforated after compaction to reduce their flow resistance.

59. The method according to claim 57, characterized in that the perforation takes place by needling the compact material layer.

60. The method according to any one of claims 54 to 56, characterized in that the fleece is melted in a Oberfächenbereich to produce a skin formation of the material layer.